Gage pressure transducer and method for making the same

ABSTRACT

A gage pressure transducer comprising a first pressure sensing assembly exposed to a main pressure and a second pressure sensing assembly exposed to a reference pressure. The pressure sensing assemblies comprise half-bridge sensors and means for using an alignment glass plate with each sensor which reduces the amount of oil required for operation, which consequently reduces the back pressures caused by large volumes of oil. The pressure sensor assemblies are hermetically sealed using glass frits, therefore enabling the gage pressure transducer to robustly and accurately measure pressure in harsh environments.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application claiming priority to U.S.patent application Ser. No. 12/971,615, filed Dec. 17, 2010, thecontents of which are hereby incorporated by reference as if fully setforth herein.

TECHNICAL FIELD

The present invention relates to gage pressure transducers, and moreparticularly to a gage pressure transducer comprising a plurality ofpressure sensing assemblies in a single housing.

BACKGROUND

Gage pressure transducers are often used to measure gage/differentialpressures in harsh environments. Generally, gage pressure transducerscomprise two pressure sensing assemblies, with one pressure sensingassembly being exposed to a main pressure and the other being exposed toa reference pressure. Each pressure sensing assembly includes ahalf-bridge sensor such that when they combine together, they provide agage pressure measurement of the environment to be measured.

Many of the gage pressure transducer assemblies of the prior art,however, present shortcomings that interfere with the accuracy of thegage pressure measurement. For example, some embodiments utilize non-oilfilled pressure capsules contained in a non-hermetic gage transducerassembly. The non-hermeticity of this gage transducer assembly enablesthe harsh environment to interfere with the operation of the transducerassembly, which consequently may adversely affect the accuracy of theoverall gage pressure measurement. In another example, other embodimentsutilize wire-bonded oil filled pressure capsules, which require largevolumes of oil to operate. Large volumes of oil, however, causesignificant back pressure against the deflecting diaphragm, which alsointerferes with the accuracy of the overall gage pressure measurement.

Accordingly, there is a need for a gage pressure transducer assemblythat utilizes hermetically sealed pressure sensing assemblies such thatharsh environments do not interfere with the operation and, further, anassembly that utilizes minimal oil, such that back pressures associatedwith large oil volumes can be reduced.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide a miniaturized,hermetically sealed gage transducer assembly, and a method for makingthe same, comprising: a housing having a first section and a secondsection, a first sensing assembly housed in the first section, the firstsensing assembly being exposed to a main pressure, and a second sensingassembly housed in the second section, the second sensing assembly beingexposed to a reference pressure, and an oil region that is less thanapproximately 0.015 inches. The first sensing assembly and the secondsensing assembly may be leadless. Further, the first and second sensingassemblies may be substantially identical in configuration and inelectrical communication with each other.

More specifically, the first and second sensing assemblies may eachcomprise a half-bridge piezoresistive sensing network that electricallycommunicate with each other to form a complete Wheatstone Bridge.

Even more specifically, the sensing assemblies may comprise: a headershell; a glass pre-form configured to fit within the header shell, theglass pre-form comprising a plurality of pin apertures and an oil tubeaperture; a plurality of header pins, each extending through one of theplurality of pin apertures past a top surface of the glass pre-form; anoil tube extending through the oil tube aperture past the top surface ofthe glass pre-form; a sensor mounted onto a top surface of the glasspre-form, wherein the sensor comprises electrical contact pads that arealigned and in electrical communication with the header pins; adiaphragm mounted on a top surface of the header shell such that it isabove the sensor; wherein the oil region is disposed between thediaphragm and the sensor, wherein the oil tube provides oil to the oilregion. The sensing assemblies may further comprise an alignment glassplate mounted onto the top surface of the glass pre-form, comprising afirst aperture for encircling the oil tube and a second aperture forencircling the sensor.

To hermetically seal the device, glass frits may be used to secure thebonding between the header pins and the electrical contact pads, thesensor and the glass pre-form, and the alignment glass plate and theglass pre-form.

Further, the header shell can comprise an outwardly extending flangeadapted to secure and hermetically seal the first and second sensingassemblies into the first and second sections, respectively.

The resultant device is a miniaturized, hermetically sealed gagepressure transducer comprising sensing assemblies that, in combination,accurately measure gage pressure in harsh environments withoutinterference from back pressures caused by large oil volumes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a gage pressure transducer assembly comprising twopressure sensing assemblies according to an aspect of the presentinvention.

FIG. 2 illustrates a combined Wheatstone Bridge according to an aspectof the present invention.

FIG. 3 provides a cross-sectional illustration of a leadless pressuresensing assembly according to an aspect of the present invention.

FIG. 4 provides a top view illustration of an alignment glass plateaccording to an aspect of the present invention.

FIG. 5 provides a cross-sectional illustration of the pressure sensingassembly according to an aspect of the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numerals represent likeelements, exemplary embodiments of the present invention are hereindescribed. It is to be understood that the figures and descriptions ofthe present invention have been simplified to illustrate elements thatare relevant for a clear understanding of the present invention, whileeliminating, for purposes of clarity, many other elements found intypical gage pressure transducers and methods of making and using thesame. Those of ordinary skill in the art will recognize that otherelements are desirable and/or required in order to implement the presentinvention. However, because such elements are well known in the art, andbecause they do not facilitate a better understanding of the presentinvention, a discussion of such elements is not provided herein.

Referring to FIG. 1, there is shown a gage pressure transducer assembly100 having a first section 105 and a second section 110. A firstpressure sensing assembly 115 is housed in the first section 105 and asecond pressure sensing assembly 120 is housed in the second section110. The first pressure sensing assembly 115 and the second pressuresensing assembly 120 may be fit within their respective pressure ports,which are defined within the gage pressure transducer assembly 100. Thefirst 115 and second 120 pressure sensing assemblies are welded withinthe pressure ports such that they are hermetically sealed within thepressure ports. The hermetic sealing enables the gage pressuretransducer assembly 100 to accurately measure pressures in harshenvironment applications without interference from the environment.

In various embodiments of the present invention, the gage pressuretransducer assembly 100 is miniaturized. This miniaturization isachieved by utilizing pressure sensing assemblies 115/120, which may beleadless and are described further herein. In one example, the length ofthe first section 105 is approximately 0.395 inches and the width isapproximately 0.25 inches. In another example, the length of the secondsection 110 is approximately 0.960 inches and the width is approximately0.625 inches. The embodiments of the present invention, however, are notlimited to these dimensions and can be of many dimensions.

The first pressure sensing assembly 115 of the present invention may beexposed to a main (external) pressure, while the second pressure sensingassembly 120 may be exposed to a reference (absolute) pressure. Both thefirst pressure sensing assembly 115 and the second pressure sensingassembly 120 comprise a half-bridge piezoresistive sensing network andelectrically communicate with each other to form a complete Wheatstonebridge, as illustrated in FIG. 2. The Wheatstone Bridge subtracts thereference pressure from the main pressure, which therefore provides anaccurate gage pressure measurement.

Referring to FIG. 3, there is shown an embodiment of the first 115 andsecond 120 pressure sensing assemblies, which are substantiallyidentical in configuration. The first 115 and second 120 pressuresensing assemblies generally comprise a leadless sensor 305, a leadlessheader assembly 310, and a metal diaphragm 325. More specifically, themetal diaphragm 325 is secured to the header assembly 310 and covers thetop portion of the leadless sensor 305, which is also secured to theheader assembly. Further, the first 115 and second 120 pressure sensingassemblies comprise an oil region 320 disposed between the metaldiaphragm 325 and the sensor 305. This general configuration of thefirst 115 and second 120 pressure sensing assemblies utilizes less oilin comparison to designs in the prior art. Less oil utilization reducesback pressures caused by large amounts of oil, and therefore optimizesthe overall transducer performance and enables its size to beminiaturized.

The header assembly 310 comprises a header shell 330, a glass pre-form335, header pins 345, and an oil tube 315. The exterior of the headershell 330 has an outwardly extending flange 360, which enables thewelding of the header assembly 310 into the respective pressure portsdefined within the gage pressure transducer assembly 100. Thisconfiguration further facilitates complete hermetic sealing of the gagepressure transducer assembly 100, which enables superior pressuretransmission to the sensors 305 of the first 115 and second 120 pressuresensing assemblies.

The glass pre-form 335 is configured to fit within the header shell 330.In various embodiments, the glass pre-form 335 comprises a plurality ofpin apertures 340 and an oil tube aperture 350. The pin apertures 340are configured to receive header pins 345 are adapted to electricallycommunicate with the sensor 305. In some embodiments, the header pins345 may have a diameter of approximately 0.01 inches and may extendapproximately 0.005 inches from the top surface of the glass pre-form335 to make contact with contact terminals located on the sensor 305.The header pins 345 are not limited to these dimensions, however.

The oil tube aperture 350 is configured to receive the oil tube 315,which provides oil to the oil region 320 located between the metaldiaphragm 325 and the sensor 305. In some embodiments, the oil tube 315is approximately 0.03 inches in diameter, however other embodiments maycomprise oil tubes of different dimensions.

Referring to FIG. 4, there is shown an alignment glass plate 355. Thisalignment glass plate 355 helps to align the sensor 305 of the first 115and second 120 pressure sensing assemblies. The alignment glass plate355 defines a centralized first aperture 405 and a second aperture 410.The first aperture 405 is substantially square-shaped in cross sectionand configured to accommodate the sensor 305, such that it covers thesides of the sensor 305. It should be understood that because the firstaperture 405 cooperatingly accommodates the sensor 305, it thereforetakes on the approximate shape and dimensions of the sensor 305. Thesecond aperture 410 is configured to encircle the oil tube 315.Accordingly, the second aperture 410 is substantially circular-shaped incross section and takes on the approximate shape and dimensions of theoil tube 315.

As illustrated in FIG. 3, the alignment glass plate 355 may have adiameter substantially equal to the diameter of the glass pre-form 335,such that the alignment glass plate 355 may be aligned and mounted tothe glass pre-form 335. To secure the attachment of the alignment glassplate 355 to the glass pre-form 335, a non-conductive glass frit may beused to enhance the bonding, which fills into small spaces between thealignment glass plate 355 and the glass pre-form 335. FIG. 5 illustratesthe alignment glass plate 355 mounted onto the glass pre-form 335,wherein glass frit 505 is used to enhance the bonding.

The bottom of the sensor 305 may also be mounted onto the glass pre-form335. A non-conductive glass frit may be used to enhance the bondingbetween the bottom of the sensor 305 and the glass pre-form 335. Aconductive glass frit may be used to bond the header pins 345 to thecontact terminals on the sensor 305, such to enable electricalcommunication between the header pins 345 and the sensor 305. Thenon-conductive glass frit enhances bonding by filling in voids betweenthe sensor 305 and the glass pre-form 335, and the conductive glass fritenhanced bonding between the header pins 345 and the contact terminalson the sensor 305.

Referring back to FIG. 3, the metal diaphragm 325 may be mounted ontothe header shell 330 such that it is positioned above the sensor 305 andthe alignment glass plate 355. Disposed between the metal diaphragm 325and the sensor 305 and the alignment glass plate 355 is an oil region320, wherein oil from the oil tube 315 may be deposited.

Many of the embodiments of the prior art do not comprise gold bonds orgold wires, therefore enabling the size of the oil region 320 to bedrastically reduced in comparison to oil regions of the prior art. Theoil region 320 of the present invention, for example, may be less thanapproximately 0.015 inches, and more specifically may be between 0.001to 0.002 inches in thickness. Such reduced dimensions reduce the amountof oil required for the first and second pressure sensing assemblies115/120 by at least an order of magnitude in comparison to thenon-leadless oil filled sensors of the prior art.

The reduced oil volume correspondingly reduces the back pressureassociated with the oil, which may be calculated using the equationbelow:

$P = \frac{16V\; E\; t^{3}}{{\pi\left( {1 - v^{2}} \right)}a^{6}}$where V is the expanded volume of the oil, t is the thickness of thediaphragm, E is Young's modulus of the diaphragm, ν is Poisson's ratio,and α is the radius of the diaphragm. The reduced back pressure enablesthe gage pressure transducer 100 to accurately measure gage pressures atvery low pressures, for example, below 5 psi.

The resultant device is a miniaturized, hermetically sealed gagepressure transducer comprising pressure sensing assemblies that, incombination, accurately measure gage pressure in harsh environmentswithout interference from back pressures caused by large oil volumes.

The invention claimed is:
 1. A gage transducer assembly, comprising: afirst sensing assembly housed in a first section of a housing, the firstsensing assembly being exposed to a first pressure and comprising afirst half-bridge piezoresistive sensing network; a second sensingassembly housed in a second section of a housing, the second sensingassembly being exposed to a second pressure and comprising a secondhalf-bridge piezoresistive sensing network; and an oil region less than0.015 inches in thickness.
 2. The assembly of claim 1, the first andsecond sensing assemblies being substantially identical inconfiguration.
 3. The assembly of claim 1, wherein the first pressure isa main pressure and the second pressure is a reference pressure.
 4. Theassembly of claim 1, wherein the first half-bridge piezoresistivesensing network and the second half-bridge piezoresistive sensingnetwork are in electrical communication with each other to form acomplete Wheatstone bridge.
 5. The assembly of claim 1, wherein thefirst and second sensing assemblies each comprise: an alignment platehaving an oil tube alignment aperture and a sensor accommodatingaperture; a sensor module inserted into the sensor accommodatingaperture; a header surrounding the alignment plate, the header having aprotruding top surface; and a diaphragm disposed on the protruding topsurface of the header to create the oil region defined above the sensormodule and between the diaphragm and the alignment plate, wherein theprotruding top surface encapsulates the oil region.
 6. The assembly ofclaim 5, wherein the first and second sensing assemblies furthercomprise a pre-form having a plurality of pin accommodating aperturesand an oil tube accommodating aperture aligned with the oil tubealignment aperture, wherein the alignment plate is disposed on the topsurface of the pre-form.
 7. The assembly of claim 6, wherein thealignment plate is secured to the pre-form using a non-conductive glassfrit.
 8. The assembly of claim 5, wherein the header comprises anoutwardly extending flange adapted to secure and hermetically seal thefirst and second sensing assemblies into the first and second sectionsof the housing, respectively.
 9. The assembly of claim 1, wherein theoil region is between about 0.001 and 0.002 inches in thickness.
 10. Agage transducer assembly, comprising: a first sensing assembly housed ina first section of a housing, the first sensing assembly comprising afirst half-bridge piezoresistive sensing network; and a second sensingassembly housed in a second section of a housing, the second sensingassembly comprising a second half-bridge piezoresistive sensing network;wherein the first and second sensing assemblies are substantiallyidentical in configuration and further wherein the first half-bridgepiezoresistive sensing network and the second half-bridge piezoresistivesensing network are in electrical communication with each other to forma complete Wheatstone bridge.
 11. The assembly of claim 10, wherein thefirst and second sensing assemblies each comprise: an alignment platehaving an oil tube alignment aperture and a sensor accommodatingaperture; a sensor module inserted into the sensor accommodatingaperture; a header surrounding the alignment plate, the header having aprotruding top surface; and a diaphragm disposed on the protruding topsurface of the header to create an oil region defined above the sensormodule and between the diaphragm and the alignment plate, wherein theprotruding top surface encapsulates the oil region.
 12. The assembly ofclaim 11, wherein the oil region is less than 0.015 inches in thickness.13. The assembly of claim 12, wherein the oil region is between about0.001 and 0.002 inches in thickness.
 14. The assembly of claim 11,wherein the first and second sensing assemblies further comprise apre-form having a plurality of pin accommodating apertures and an oiltube accommodating aperture aligned with the oil tube alignmentaperture, wherein the alignment plate is disposed on the top surface ofthe pre-form.
 15. The assembly of claim 14, wherein the alignment plateis secured to the pre-form using a non-conductive glass frit.
 16. Theassembly of claim 11, wherein the header comprises an outwardlyextending flange adapted to secure and hermetically seal the first andsecond sensing assemblies into the first and second sections of thehousing, respectively.
 17. A method of making an oil-filled pressuretransducer, comprising: preparing substantially identical first andsecond leadless sensor assemblies, comprising: mounting an alignmentplate within a header shell having a protruding top surface, wherein thealignment plate has an oil tube alignment aperture and a sensoraccommodating aperture; inserting a sensor module comprising ahalf-bridge sensing element into the sensor accommodating aperture ofthe alignment plate; mounting a diaphragm to the protruding top surfaceof the header shell, such that an oil accommodating region is definedabove the sensor module and between the diaphragm and the alignmentplate; and welding the first and second leadless sensor assemblies intofirst and second sections of a housing, respectively.
 18. The method ofclaim 17, wherein the oil accommodating region is less than 0.015 inchesin thickness.
 19. The method of claim 18, wherein the oil accommodatingregion is between about 0.001 inches and 0.002 inches in thickness. 20.The method of claim 17, wherein the half bridge sensing element of thefirst and second leadless sensor assemblies electrically communicate toform a full Wheatstone bridge.